terminology and guidelines for glaucoma ii - Kwaliteitskoepel

In case of a narrow approach, it is possible to improve the visualization of the angle recess by having the patient rotate
the globes towards the mirror being used.
Problems
Related to the technique
The most widely used technique is indirect gonioscopy where the angle is viewed in a mirror of the lens. The position of the
globe is influential. If the patient looks in the direction opposite of the mirror the angle appears narrower and viceversa.
A second pitfall is related to the degree of pressure of the lens against the cornea and especially occurs when the diameter of
the lens is smaller than the corneal diameter (as with the small Goldmann lens, the Posner or the Zeiss lenses). This effect is
useful for indentation or dynamic gonioscopy with the Posner or Zeiss lenses; inadvertent pressure over the cornea however,
will push back the iris, and gives an erroneously wide appearance to the angle. With the Goldman lens indentation is transmitted
to the periphery of the cornea and narrows the angle.
Related to the anatomy
Recognition of angle structures may be impaired by variations in the anterior segment structures like poor pigmentation, iris
convexity or existence of pathological structures. The examiner should be familiar with all the anatomical structures of the
angle: Schwalbe’s line, trabecular meshwork, scleral spur, ciliary band and iris.
Pharmacological mydriasis
Dilation of the pupil with topical or systemic drugs can trigger iridotrabecular contact or pupillary block, eventually leading
to angle-closure. Angle-closure attacks can occur, even bilaterally, in patients treated with systemic parasympatholytics
before, during or after abdominal surgery and has been reported with a serotonergic appetite suppressant.
Although pharmacological mydriasis with topical tropicamide and neosynephrine is safe in the general population even in
eyes with very narrow approach, in occasional patients raised IOP and an angle occlusion can be observed.
Theoretically, although any psychoactive drugs have the potential to cause angle-closure, it is unlikely that pre-treatment
gonioscopy findings alone are of help to rule out such risk. In eyes with narrow angles, it makes sense to repeat gonioscopy
and tonometry after initiation of treatment. Prophylactic laser iridotomy needs to be evaluated against the risks of
angle-closure or of withdrawal of the systemic treatment. (See Chapter 2 - 4). None of these drugs is contraindicated per
se in open-angle glaucoma.
Ciliochoroidal detachment with bilateral angle-closure has been reported after oral sulfa drugs.
Since patients most commonly have mixed components of angle-closure, gonioscopic appearances are seldom clear-cut as
far as determining the etiology.
The visualization during gonioscopy of the ciliary processes through the undilated pupil is a sign of forward displacement
of the iris and of the anterior lens surface, associated with anterior rotation of the ciliary body.
1.2.3 - GRADING
The use of a grading system for gonioscopy is highly desirable 2,5,6 . It stimulates the observer to use a systematic approach in
evaluating angle anatomy, it allows comparison of findings at different times in the same patients, or to classify different
patients.
A grading method is also very helpful to record the gonioscopy findings and should always be used on patients’ charts.
The Spaeth gonioscopy grading system is the only descriptive method including all the parameters described above (chapter
1.2.1) 2 . Other grading systems are useful though less specific. There are several gonioscopy classification systems; we list the
most widespread.
Slit lamp-grading of peripheral AC depth - the Van Herick method 7
Grade 0 represents iridocorneal contact.
A space between iris and corneal endothelium of < 1/4 corneal thickness, is a grade I.
When the space is ≥ 1/4 < 1/2 corneal thickness the grade is II.
A grade III is considered not occludable, with an irido/endothelial distance ≥ 1/2 corneal thickness.
This technique is based on the use of corneal thickness as a unit measure of the depth of the anterior
chamber at furtherest periphery. This method is very useful if a goniolens is not available 7,8 .
Ch. 1 - 12 EGS